The present application relates to gas sensors and particularly to a gas sensor which optically senses the concentration of a diamagnetic or paramagnetic gas in a gaseous mixture.
There are several commercial instruments on the market which measure the quantity of gas present by magnetic force methods. These techniques rely on the fact that when a paramagnetic or diamagnetic material is subjected to a magnetic field, these materials experience a force which is proportional to the applied magnetic field squared, i.e., H.sup.2. The constant of proportionality is the product of the sample volume (number of molecules present) and magnetic susceptibility. Several experimental arrangements are currently employed which include the Faraday and the Gouy methods which are described in the book "Introduction to Magnetic Materials" by B. D. Cullity, Chapter 2, pp. 74-78 (1972). In general, these methods include measuring the force generated by the gas sample in the presence of the magnetic field and in some cases balancing out the force by a counter-applied force. Generally, electrical pick-up techniques are used to measure the force. Once the force is measured, when the applied field is known, then the presence of a diamagnetic or paramagnetic gas may be determined if the susceptibility of the gas is known.
The force equation in its most general form is given by: EQU F=(K-K.sub.o)a H.sup.2 /2,
where K and K.sub.o are the susceptibilities of the material (gas) to be detected and of the background median, respectively, a is the cross-sectional area of the sample and H is the applied magnetic field. Because of the small size of the susceptibilities involved and electronic noise, the precision or accuracy of these measurements is limited. Furthermore, remote detection and/or analysis is limited because of the difficulty in performing high precision measurements electronically at any substantial distances. Electromagnetic pickup techniques severely limit the environments in which remote sensing is possible and are restricted to non-explosive and low electromagnetic interference (EMI) environments.